1. Field of the Invention
This invention relates generally to motorcycles. More particularly, the invention pertains to an exhaust gas recirculation (EGR) system for a motorcycle engine.
2. General Background
A typical motorcycle comprises an exposed engine and, in many cases, the engine is the primary visual focal point of a motorcycle. As such, aesthetics is typically a primary concern in design of a motorcycle engine. For that reason, almost every part of a motorcycle engine, from the intake manifold to the exhaust system, is configured to be visually appealing. Nonetheless, motorcycle engines necessarily must comprise key components to operate, which in some cases negatively impact the aesthetics of the motorcycle engines. For this reason, motorcycle designers and owners often avoid adding beneficial, but unnecessary, components and systems to motorcycle engines.
An example of a beneficial, but non-critical, engine component is an EGR system. EGR systems reduce nitrogen oxide emissions by recirculating a portion of the exhaust gases into the intake system. The recirculated exhaust gases increase the specific heat capacity of the gases flowing into combustion chambers and thereby reduce combustion temperature. Reduced combustion temperature reduces nitrogen oxide production. Most modern EGR systems comprise an EGR valve, which controls the amount and timing of exhaust gas recirculation such that the impact of EGR systems on engine performance is virtually negligible.
Despite the benefits of EGR systems in reducing harmful emissions, most motorcycle engines lack such systems due to the negative impact such systems can have on the overall aesthetics of motorcycle engines. This is because EGR systems typically comprise tubing that is external to the cylinder heads for channeling exhaust gases from the exhaust system and to the intake system. Such tubing is often seen as being aesthetically unpleasing.
Despite the aesthetically unpleasing nature of EGR systems, increasing emission standards makes such systems more desirable. This is particularly true for carbureted engines, which tend to have worse emissions as compared to fuel injected engines.